1. Field of the Invention
This invention relates generally to voltage regulators, and more particularly to a charge pump based voltage regulator with smart power regulation.
2. Description of the Prior Art
A conventional SRAM device employs SRAM cells, each cell consisting of four or six transistors. A thyristor based SRAM cell consists of only two devices, the thyristor itself, and a pass transistor. An SRAM device comprising thyristor SRAM cells will thus be much more compact and much less costly.
Switching between the on state and the off state of a thyristor however, takes rather a long time due to the long life time of the minority carriers in the P-base. This characteristic undesirably limits the speed of operation of a thyristor-based SRAM. A thinly capacitively coupled thyristor (TCCT) to significantly speed up the switching has been disclosed in U.S. Pat. No. 6,229,161, entitled Semiconductor capacitively-coupled NDR Device And Its Applications In High-Density High-Speed Memories And In Power Switches, issued May 8, 2001 to Nemati et al. A TCCT employs an additional gate closely coupled to a base region. This gate is coupled to a control line commonly known as word line 2 (WL2), which is pulsed from a negative voltage to a positive voltage when the TCCT is in its write operation. The negative voltage is necessary to lower the P-base potential and allows the carriers in the P-base to flow out quickly during the write operation, significantly expediting the switching of TCCT states. FIG. 1 illustrates a TCCT cell in a CMOS process.
Conventional SRAM products based on six-MOSFET memory cells are powered-up by a positive voltage supply and usually do not require a negative voltage source to operate.
It would therefore be desirable and advantageous in view of the foregoing to provide a technique to generate an on-chip negative supply for the WL2 in a TCCT-based SRAM array from the positive voltage supply powering-up the integrated circuit (IC).